A pressurized-water reactor connects with one or more steam generators via a main coolant loop through which pressurized-water coolant is circulated by a main coolant pump. A flow of coolant is removed from the coolant circulating in the loop, passed through a treatment system and returned to the coolant circulating in the loop. To avoid the need for extensive adjustment of control rods in the reactor's core, the coolant is provided with a controlled boron content, in the form of boric acid. To hold the coolant's boron content at the desired concentration, the treatment system includes a recification column through which the removed flow is passed and where by fractional distillation or rectification, the boric acid is removed from the removed coolant flow as required. Thereafter, if required, the substantially boron-free coolant may have boric acid added to it to provide the desired boron content required to adjust the activity of the core, this practice usually being called chemical trimming of the core. The boron concentration required for chemical trimming is relatively low.
During the reactor operation, the coolant becomes gassed, and another function of the coolant treatment system is to degassify the coolant, the system, therefore, including a gas separator or degassification apparatus. Other equipment may be included by the system.
Heretofore the system has been organized so that the coolant flow removed from the circulating coolant in the loop, is passed through the gas separator first, for degassification, and then through the rectification column where substantially all of the boron, in the form of boric acid, is removed from the flow, the boron content required for the chemical trimming then being added to the flow under treatment and the flow returned to the coolant circulating in the loop. The flow passed through the treatment system is small in relation to the flow of the coolant circulating in the loop, but the treatment system can be operated continuously to maintain the coolant in the loop in the desired condition. The gas separator requires heating of the coolant and cooling of the separator's reflux condenser and cooling of the separated gas prior to its disposal such as via the reactor plant gas disposal stack, after interposed gas treated, if required, for atmospheric pollution control. Therefore, the operation of the separator involves the expense of the steam and cooling water, and occasionally it may be necessary to service the gas separator requiring it to be shut down, in which event the entire treatment system is put out of operation during the servicing period.
It follows from the foregoing that the operation of the treatment system involves the problems imposed by the possibility of a complete shut-down of the entire system and of the expense of the operation of the gas separator component, as well as the need for precision equipment for metering into the rectified flow the boric acid required to maintain the desired boron concentration for the chemical trimming of the reactor core, in the main body of coolant circulating in the loop.